CN112469938A

CN112469938A - Threaded joint for steel pipe

Info

Publication number: CN112469938A
Application number: CN201980044975.5A
Authority: CN
Inventors: 奥洋介; 堂内贞男
Original assignee: Vallourec Oil and Gas France SAS; Nippon Steel and Sumitomo Metal Corp
Current assignee: Vallourec Oil and Gas France SAS; Nippon Steel Corp
Priority date: 2018-10-11
Filing date: 2019-07-24
Publication date: 2021-03-09
Anticipated expiration: 2039-07-24
Also published as: AR116681A1; WO2020075365A1; SA520420520B1; MX2020014227A; JPWO2020075365A1; EP3865752B1; BR112021000168A2; BR112021000168B1; EP3865752A4; CN112469938B; CA3122795A1; JP7189961B2; EP3865752A1; RU2759043C1; US20210246737A1; CA3122795C; US11391097B2

Abstract

Provided is a threaded joint for a steel pipe, which can achieve both high torque performance and high tensile performance. A threaded joint (1) comprises: a tubular male buckle (10) formed at one tip end portion of the steel pipe; and a tubular female buckle (20) for inserting the male buckle (10) and fastening the male buckle (10). The pin (10) includes an external thread (11), and the external thread (11) is formed on the outer periphery of the pin (10) and is formed of a wedge thread. The box (20) includes an internal thread (21), the internal thread (21) corresponding to the external thread (11), formed on the inner periphery of the box (20), and formed of a wedge thread. The threaded joint (1) satisfies the following formula (1). In the formula (1), LP represents the pitch between the load surfaces (111) of the male screw (11), and SP represents the pitch between the insertion surfaces (112) of the male screw (11). 3 percent to 8 percent (LP-SP)/LP (1).

Description

Threaded joint for steel pipe

Technical Field

The present disclosure relates to a threaded joint for steel pipes.

Background

For example, steel pipes called oil well pipes are used for exploration and production of oil wells, gas wells (hereinafter, collectively referred to as "oil wells"), development of unconventional resources such as oil sands and shale gas, recovery and storage of carbon dioxide (ccs), geothermal power generation, hot springs, and the like. Threaded joints are used to connect the steel pipes.

The form of such a threaded joint for steel pipes is roughly classified into a combination type and an integral type. In the combined type, one of the pair of pipes to be connected is a steel pipe, and the other pipe is a pipe joint. In this case, male screws are formed on the outer peripheries of both end portions of the steel pipe, and female screws are formed on the inner peripheries of both end portions of the pipe joint. Then, the male screw of the steel pipe is screwed into the female screw of the pipe joint, and the two are fastened and coupled. In the integral type, both of the pair of pipes to be connected are steel pipes, and no separate pipe joint is used. In this case, a male screw is formed on the outer periphery of one end portion of the steel pipe, and a female screw is formed on the inner periphery of the other end portion. The male screw of one steel pipe is screwed into the female screw of the other steel pipe, and the two pipes are fastened and connected.

Generally, a joint portion of a pipe end formed with an external thread includes an element to insert an internal thread, and thus is called a "pin". On the other hand, the joint portion of the pipe end formed with the internal thread includes an element that receives the external thread, and is therefore called a "box". The male buckle and the female buckle are end parts of the pipe, and are both tubular.

For example, in a threaded joint used for a deep oil well, a large tensile load due to the self weight of an oil country tubular good is applied to a shallow portion, and a large compressive load due to thermal expansion is applied to a deep portion.

A threaded joint using wedge threads is disclosed in U.S. reissue patent No. 30647 specification (patent document 1), U.S. invention patent No. 6158785 specification (patent document 2), and international publication No. WO2015/194193 (patent document 3). The width of the thread ridge of the wedge thread gradually changes along the direction of the helix. Wedge threads, also known as dovetail threads, enable higher torque performance. However, none of patent documents 1 to 3 describe the rate of change in the thread width of a wedge thread.

Japanese patent publication No. 2012-512347 (patent document 4) also discloses a threaded joint using a wedge thread. Near both ends of the external thread region, the lead between the male thread stabbing flanks and the lead between the male thread load flanks are constant. Similarly, in the vicinity of both ends of the female thread region, the lead between the female thread stabbing flanks and the lead between the female thread load flanks are constant. Thus, the thread width is constant near both ends of the threaded region. Although it is recognized that there is a difference between the lead between the load flanks and the lead between the stabbing flanks, no specific numerical value of the difference is described at all.

The present specification refers to the following prior art documents.

Patent document 1: united states reissue invention patent No. 30647 specification

Patent document 2: specification of U.S. patent No. 6158785

Patent document 3: international publication No. WO2015/194193

Patent document 4: japanese Kohyo publication No. 2012-512347

Disclosure of Invention

Since the load surface and the insertion surface of the wedge thread have negative profile half angles, the wedge thread is engaged at the time of tightening to exhibit high torque performance. In addition, in the wedge thread, the thread width may become narrower as it approaches the tip of the pin or the box in order to facilitate fastening. In other words, there is a difference between the load face pitch and the stab face pitch. This difference in pitch is referred to as the "lead variable (delta lead)". The lead variables determine the thread width near the tip of the pin and box.

In some cases, "Wedge Ratio (Wedge Ratio)" is used instead of the lead variable in consideration of the influence caused by the absolute value of the pitch. Wedge ratio is the value of the lead variable divided by the load face pitch and is therefore expressed as a percentage of the ratio of the lead variable to the load face pitch.

A larger wedge ratio indicates a larger reduction rate of the thread width. If the wedge ratio is large, the thread width becomes narrow near the tip of the pin and the box. If the thread width is narrow, the wedge thread cannot withstand a large tensile load, and the thread itself may be broken. Therefore, attention is required in setting the wedge ratio. Hereinafter, the property of the wedge thread that can withstand tensile load is referred to as "tensile property".

Patent document 4 (japanese unexamined patent publication No. 2012 and 512347) discloses the optimization of the wedge ratio. However, there is no document in which the influence of the wedge ratio on the torque performance is evaluated in addition to the influence of the wedge ratio on the tensile performance.

An object of the present disclosure is to provide a threaded joint for a steel pipe that can achieve both high torque performance and high tensile performance.

The present inventors have conducted intensive studies on an appropriate wedge ratio for simultaneously improving the torque performance and the tensile performance, and as a result, have found that: by changing the wedge ratio, higher torque performance and higher tensile performance can be considered at the same time.

The threaded joint for a steel pipe of the present disclosure includes a tubular pin and a tubular box. A tubular male buckle is formed at one top end portion of the steel pipe. The tubular female buckle is used for the male buckle to insert and fasten with the male buckle. The pin includes external threads. The external thread is formed on the outer periphery of the pin and is composed of a wedge thread. The box includes internal threads. The internal thread corresponds to the external thread, is formed on the inner periphery of the box and is formed by wedge threads. The threaded joint satisfies the following formula (1).

3％≤(LP－SP)/LP≤8％(1)

In equation (1), LP is the pitch between the load faces of the external threads. SP is the pitch between the stabbing faces of the external thread.

Drawings

Fig. 1 is a longitudinal sectional view of a threaded joint for steel pipes according to an embodiment along a pipe axis direction.

Fig. 2 is a longitudinal sectional view enlarging the male and female screws in fig. 1.

Fig. 3 is a graph showing a relationship between a wedge ratio and a yield torque in the case where the load surface pitch is 8.64 mm.

Fig. 4 is a graph showing a relationship between a wedge ratio and a yield torque in the case where the load surface pitch is 10.8 mm.

Fig. 5 is a graph showing a relationship between a wedge ratio and a yield torque in the case where the load surface pitch is 7.2 mm.

Fig. 6 is a graph showing a relationship between a wedge ratio and an equivalent plastic strain in the case where the load surface pitch is 8.64 mm.

Fig. 7 is a graph showing a relationship between a wedge ratio and an equivalent plastic strain in the case where the load surface pitch is 10.8 mm.

Fig. 8 is a graph showing a relationship between a wedge ratio and an equivalent plastic strain in the case where the load surface pitch is 7.2 mm.

Detailed Description

The threaded joint for a steel pipe of the present embodiment includes a tubular pin and a tubular box. A tubular male buckle is formed at one top end portion of the steel pipe. The tubular female buckle is used for the male buckle to insert and fasten with the male buckle. The pin includes external threads. The external thread is formed on the outer periphery of the pin. Consisting of wedge threads. The box includes internal threads. The internal thread corresponds to the external thread, is formed on the inner periphery of the box and is formed by wedge threads. The threaded joint satisfies the following formula (1).

3％≤(LP－SP)/LP≤8％ (1)

Preferably, the threaded joint satisfies the following formula (2).

4％≤(LP－SP)/LP≤7％ (2)

The threaded joint may satisfy the following formula (3).

Alpha is more than or equal to-10 degrees and less than or equal to-1 degree (3)

In formula (3), α is the thread form half angle of the load face and the stabbing face of the male thread.

The male and female threads may include a complete thread portion formed of a complete thread. The complete thread portion may have a length of 40 to 60mm in the axial direction of the steel pipe.

Hereinafter, a threaded joint for a steel pipe according to the present embodiment will be described with reference to the drawings. In the drawings, the same or corresponding components are denoted by the same reference numerals, and the same description will not be repeated.

Referring to fig. 1, a threaded joint 1 for a steel pipe according to the present embodiment includes a tubular pin 10 and a tubular box 20. The male buckle 10 is formed at one tip end portion of the steel pipe 2. The female buckle 20 is inserted into the male buckle 10 and fastened with the male buckle 10. Hereinafter, the portion of the steel pipe 2 other than the tip end portion may be particularly referred to as a "steel pipe body".

The pin 10 includes an external thread 11. An external thread 11 is formed on the outer periphery of the pin 10. The box 20 comprises an internal thread 21. The female screw 21 is formed on the inner circumference of the box 20 corresponding to the male screw 11. More specifically, the male screw 11 is formed spirally on the outer periphery of the pin 10. The female screw 21 is formed spirally on the inner periphery of the box 20. The external thread 11 and the internal thread 21 are constituted by tapered threads. The external thread 11 and the internal thread 21 are also formed by wedge threads.

Referring to fig. 2, the load face 111 of the male thread 11 and the load face 211 of the female thread 21 have a thread form half angle α. The insertion face 112 of the male thread 11 and the insertion face 212 of the female thread 21 have a thread form half angle β. The profile half angle α is an angle of the load surfaces 111 and 211 with respect to a plane VP perpendicular to the pipe axis (the axis of the steel pipe 2) TA. The profile half angle β is the angle of the

insertion face

112, 212 relative to a plane VP perpendicular to the tube axis TA. In the case where the

load face

111, 211 or the

insertion face

112, 212 is parallel to the plane VP, the profile half angle is 0 degrees. When the load surface 111 of the male thread 11 is inclined toward the tip end side of the pin 10 with respect to the plane VP (in other words, when the load surface 211 of the female thread 21 is inclined toward the tip end side of the box 20 with respect to the plane VP), the thread form half angle α of the load surfaces 111, 211 is positive. Conversely, when the load surface 111 of the male thread 11 is inclined toward the steel pipe body of the pin 10 with respect to the plane VP (in other words, when the load surface 211 of the female thread 21 is inclined toward the steel pipe body of the box 20 with respect to the plane VP), the thread form half angle α of the load surfaces 111 and 211 is negative. In addition, when the insertion surface 112 of the male thread 11 is inclined toward the steel pipe body of the pin 10 with respect to the plane VP (in other words, when the insertion surface 212 of the female thread 21 is inclined toward the pipe body of the box 20 with respect to the plane VP), the tooth form half angle of the insertion surfaces 112 and 212 is positive. Conversely, when the insertion surface 112 of the male thread 11 is inclined toward the tip end side of the pin 10 with respect to the plane VP (in other words, when the insertion surface 212 of the female thread 21 is inclined toward the tip end side of the box 20 with respect to the plane VP), the profile half angle of the insertion surfaces 112, 212 is negative. The profile half angles alpha and beta of the wedge thread are both negative.

The male thread 11 and the female thread 21 are preferably formed of a complete thread, and an incomplete thread is not present. When all the

threads

11, 21 are formed of full threads, the contact area between the male thread 11 and the female thread 21 increases, and the torque performance improves. The length of the complete thread portion (the male thread 11 and the female thread 21 formed by the complete thread) is, for example, 40 to 60 mm.

The threaded joint 1 for a steel pipe satisfies the following formula (1).

3％≤(LP－SP)/LP≤8％ (1)

Preferably, the threaded joint for steel pipes 1 satisfies the following formula (2).

4％≤(LP－SP)/LP≤7％ (2)

In equations (1) and (2), LP is the pitch between the load surfaces 111 of the male screw 11 (hereinafter referred to as "load surface pitch"). SP is a pitch between the stabbing faces 112 of the male screw thread 11 (hereinafter referred to as "stabbing face pitch"). (LP-SP)/LP represents the wedge rate. The load face pitch LP is equal to the pitch between the load faces 211 of the internal threads 21. The pitch SP of the stabbing surfaces is equal to the pitch between the stabbing surfaces 212 of the female threads 21.

That is, the upper limit of the wedge ratio is 8%, preferably 7%. The lower limit of the wedge ratio is 3%, preferably 4%.

The threaded joint 1 for a steel pipe satisfies the following formula (3).

Alpha is not less than 10 degrees and not more than-1 degree, and beta is not less than-10 degrees and not more than-1 degree (3)

In formula (3), α is the thread form half angle of the load surface 111 of the male thread 11. Beta is the profile half angle of the insertion face 112 of the external thread 11. The thread form half angle α of the load surface 111 of the male thread 11 may be the same as the thread form half angle β of the stabbing surface 112 of the male thread 11, or may be different from the thread form half angle β of the stabbing surface 112 of the male thread 11. The profile half angle α of the load face 111 of the pin 11 is substantially the same as the profile half angle α of the load face 211 of the box 21. The profile half angle β of the stabbing surface 112 of the male thread 11 is substantially the same as the profile half angle β of the stabbing surface 212 of the female thread 21.

Strictly speaking, the load surface pitch LP, the insertion surface pitch SP, and the tooth form half angles α, β are used as values before fastening.

In the present embodiment, the male thread 11 and the female thread 21 are formed by wedge threads, and the wedge ratio is set to 3 to 8%, so that high torque performance and high tensile performance can be achieved at the same time.

The threaded joint 1 may be a combination type or an integral type. The combined threaded joint comprises a pipe joint and two male buttons. A male button is formed at the top end portion of a steel pipe. The other male buckle is formed at the top end part of the other steel pipe. The pipe joint comprises two female buttons. A female button is formed at one end of the pipe joint. The other female button is formed at the other end of the pipe joint. A female buckle is inserted by a male buckle and fastened with the male buckle. The other female button is formed on the opposite side of the female button and is used for inserting the other male button to be fastened with the other male button. On the other hand, the integral type threaded joint is used for connecting two steel pipes with each other, and comprises a male buckle and a female buckle. In the integral type threaded joint, one steel pipe includes a pin, and the other steel pipe 2 includes a box.

The embodiments have been described above, but the present invention is not limited to the above embodiments, and various modifications can be made without departing from the gist thereof.

Examples

To verify the effects of the present embodiment, the torque performance and the tensile performance were evaluated by a Finite Element Method (FEM). The evaluation target was a wedge type threaded joint, and the following steel pipe was used.

Size: 9-5/8 inches (tube body outside diameter: 244.48mm, tube body inside diameter: 216.8mm)

Materials: API standard oil well pipe material L80 (nominal yield strength YS 552MPa (80ksi))

Thread taper: 1/12

Length of screw thread: 50mm (male buckle), 60mm (female buckle)

Height of the thread: 1.8mm

Tooth form half angle: 5 degrees (both the load and insertion surfaces are)

Load face pitch: 7.2mm, 8.64mm or 10.8mm

Wedge ratio: 2 to 10 percent

Pitch of insertion face: inverse operation based on wedge ratio

As shown in fig. 1, the threaded joint to be evaluated is composed of only the male screw 11 and the female screw 21. The external thread 11 and the internal thread 21 are all made up of wedge threads and full threads.

Table 1 shows the dimensions and the like of 27 types of threaded joints (samples) for analysis.

[ Table 1]

In the analysis, the dimensions of the male thread 11 and the female thread 21 were changed based on the threaded joint 1 shown in fig. 1, and the torque performance and the tensile performance were evaluated.

[ evaluation of Torque Performance ]

Regarding the Torque performance, the value mtv (maximum Torque value) at which the tightening Torque starts to yield on the tightening Torque map is defined as the yield Torque, and is evaluated at this value.

[ evaluation of tensile Properties ]

With respect to tensile properties, a load equal to the tensile load with which the threaded joint 1 yields was applied to the fastened threaded joint, and the maximum value of the equivalent plastic strain generated in the root portions of the load surfaces 111, 211 and the stabbing surfaces 112, 212 of the threads located on the most apical side out of the external thread 11 and the internal thread 21 was evaluated. In the experience of the present inventors from the actual pipe test, when the equivalent plastic strain becomes about 0.08, the risk of thread breakage increases. Therefore, the tensile properties were evaluated to be excellent if the threshold value of the equivalent plastic strain was 0.08 and the value was lower than the threshold value. However, the threshold value of the equivalent plastic strain may be set to 0.070, with a greater margin in view of safety.

[ analysis results ]

Fig. 3 to 5 show values of yield torque obtained in the finite element analysis. The horizontal axis represents the wedge rate, and the vertical axis represents the MTV value corresponding to the wedge rate. Irrespective of the pitch, the MTV increases according to the wedge ratio, and particularly increases to the maximum in the region of 2-3%. From fig. 3 and 5, it can be confirmed that the MTV becomes maximum in the vicinity of the wedge ratio of 9%, and then, turns to decrease.

As a main cause of the increase in torque performance, the following is considered. This is considered to be because, if the wedge ratio is high, the thread width becomes narrow near the tip of the pin 10, and the pin 10 having a narrow thread width is fastened with the box 20 having a wide thread width, thereby generating a high contact pressure.

Fig. 6 to 8 are graphs showing the relationship between the maximum value of the equivalent plastic strain and the wedge ratio, which are generated when a tensile load is applied to the tightened threaded joint 1 as described above. This equivalent plastic strain is generated in the root portions of the load surfaces 111, 211 and the stabbing surfaces 112, 212 of the threads located on the most apical side among the external thread 11 and the internal thread 21.

The following contents are known: as shown in fig. 6, when the load surface pitch LP is 8.64mm, the maximum value of the equivalent plastic strain generated in the male thread exceeds 0.070 when the wedge ratio is 9% or more, and exceeds 0.080 when the wedge ratio is 10%.

As shown in fig. 7, when the load surface pitch LP was 10.8mm, the equivalent plastic strain did not reach 0.070 even when the wedge ratio became 10%. However, it was confirmed that the equivalent plastic strain generated in the external thread tended to increase sharply as the wedge ratio became higher.

The following contents are known: as shown in fig. 8, when the load surface pitch LP is 7.2mm, if the wedge ratio is 9% or more, the maximum value of the equivalent plastic strain generated in the male screw exceeds 0.080, and if the wedge ratio is 10%, the maximum values of the equivalent plastic strain generated in the male screw and the female screw exceed 0.080, and the possibility of thread breakage increases.

According to the above results, in order to improve the torque performance, the higher the wedge ratio, the better. However, as described above, if the wedge ratio is too high, the risk of breaking the thread near the tip of the pin (male thread) and/or the box (female thread) increases, and therefore, it is preferable that the wedge ratio be 8% or less. Further, since a reduction in the thread ridge width is equivalent to an increase in the thread groove width, and leads to an increase in the number of passes during thread cutting and a reduction in the life of the insert, an extremely high wedge ratio is also undesirable from the viewpoint of manufacturing. According to the above, the appropriate wedge ratio is 3 to 8%.

Description of the reference numerals

1. A threaded joint for steel pipes; 10. a male buckle; 11. an external thread; 20. a female buckle; 21. an internal thread; 111. 211, a load surface; 112. 212, an insertion surface; LP, load face pitch; SP, inset face pitch.

Claims

1. A threaded joint for steel pipes, wherein,

this threaded joint for steel pipe includes:

a tubular male buckle formed at one tip end portion of the steel pipe; and

a tubular female buckle into which the male buckle is inserted and fastened with the male buckle,

the pin includes an external thread formed on an outer circumference thereof and composed of a wedge thread,

the box includes an internal thread corresponding to the external thread, formed at an inner circumference of the box, and formed of a wedge thread,

the threaded joint for steel pipes satisfies the following formula (1),

3％≤(LP－SP)/LP≤8％ (1)

in equation (1), LP is the pitch between the load faces of the external thread and SP is the pitch between the stab faces of the external thread.

2. A threaded joint for steel pipes according to claim 1,

the threaded joint for steel pipes satisfies the following formula (2),

4％≤(LP－SP)/LP≤7％ (2)。

3. a threaded joint for steel pipes according to claim 1 or 2 wherein,

the threaded joint for steel pipes satisfies the following formula (3),

In formula (3), α is a thread form half angle of the load surface of the male screw thread, and β is a thread form half angle of the stabbing surface of the male screw thread.

4. A threaded joint for steel pipes as set forth in any of claims 1 to 3 wherein,

the external thread and the internal thread comprise a full thread portion composed of a full thread,

the complete thread part has a length of 40-60 mm in the axial direction of the steel pipe.